Labile affect or Pseudobulbar affect refers to the pathological expression of laughter, crying, or smiling. It is also known as "Emotional Lability", "Pathological Laughter and Crying", "Emotional Incontinence", or more recently Involuntary Emotional Expression Disorder (IEED). [1] An individual may find themselves laughing uncontrollably at something that is only moderately funny, being unable to stop themselves for several minutes. Episodes may also be mood-incongruent; an individual might laugh uncontrollably when angry or frustrated, for example.

While not as profoundly disabling as the physical symptoms of these diseases, labile affect can have a significant impact on individuals' social functioning and their relationships with others. In a disease such as Motor Neuron Disease, the majority of patients are cognitively normal; however, the appearance of uncontrollable emotions is commonly associated with learning disabilities. This may lead to severe embarrassment and avoidance of social interactions for the patient, which in turn has an impact on their coping mechanisms and their careers.